Motor-driven pumps are known and used for metering liquids to tool or other object. Typically, such pumps have a reciprocating piston actuated by a drive assembly that is connected to a motor. Various drive assemblies and connecting linkages to the piston have been described.
For example, U.S. Pat. No. 1,895,623 (Hewitt) describes a pump having a plunger that is reciprocated by an oscillatory lever connected to a cam mechanism. The lever is oscillated by the opposing forces of a downwardly biasing spring upon one end of the lever, and the rotation of an eccentric cam against the other end of the lever. Each revolution of the eccentric cam causes an upward stroke to the plunger. The plunger is then forced downwardly by means of the biasing spring.
Another reciprocating piston pump, found in U.S. Pat. No. 2,390,798 (LeClair), includes a lever connected at one end to a piston and at the other end to a plunger, is rocked back and forth by the rotation of an operating cam against a roller positioned about midway along the rocking lever. The piston is forced upwards by a coil spring, and downwards by the contact of the cam against the roller which forces the rocking lever downwards about its pivotal connection.
In yet another pump, described in U.S. Pat. No. 2,407,343 (Pyne et al.), a drive shaft carrying eccentric cams drive a series of pump pistons that pass liquid through a conduit to a plunger. A linkage connects the plunger to the pump pistons. As the liquid pressure increases, the plunger moves rearwards causing a rocking link to move a yoke forward that forces the pistons out of contact with the eccentric cams.
A drawback of each of these pumps is the use of a complex series of linkages to connect the piston with a drive assembly. Another drawback is that such pumps do not deliver a precise amount of liquid to a desired location or device. Yet another disadvantage of known pumps is that there is no indicator for showing output volume flow from the pump.
Accordingly, it would be desirable to have a motor-driven pump that has a simple design, and is capable of delivering a precise amount of lubricant or other liquid to a desired point. It would also be desirable to have a mechanism that can be set for indicating the amount of liquid being discharged from the pump.